Molecular Biology


Protocols in Current Issue
0 Q&A 148 Views Feb 5, 2023

Nucleotide excision repair (NER) removes a wide variety of structurally unrelated lesions from the genome, including UV-induced photolesions such as 6–4 pyrimidine–pyrimidone photoproducts (6-4PPs) and cyclobutane pyrimidine dimers (CPDs). NER removes lesions by excising a short stretch of single-stranded DNA containing the damaged DNA, leaving a single-stranded gap that is resynthesized in a process called unscheduled DNA synthesis (UDS). Measuring UDS after UV irradiation in non-dividing cells provides a measure of the overall NER activity, of which approximately 90% is carried out by the global genome repair (GGR) sub pathway. Here, we present a protocol for the microscopy-based analysis and quantification of UDS as a measurement for GGR activity. Following local UV-C irradiation, serum-starved human cells are supplemented with the thymidine analogue 5-ethynyl-2'-deoxyuridine (EdU), which is incorporated into repair patches following NER-dependent dual incision. The incorporated nucleotide analogue is coupled to a fluorophore using Click-iT chemistry, followed by immunodetection of CPD photolesions to simultaneously visualize both signals by fluorescence microscopy. Accompanying this protocol is a custom-built ImageJ plug-in to analyze and quantify UDS signals at sites of CPD-marked local damage. The local UDS assay enables an effective and sensitive fluorescence-based quantification of GGR activity in single cells with application in basic research to better understand the regulatory mechanism in NER, as well as in diagnostics to characterize fibroblasts from individuals with NER-deficiency disorder.


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0 Q&A 33 Views Feb 5, 2023

Chemical modifications on RNA play important roles in regulating its fate and various biological activities. However, the impact of RNA modifications varies depending on their locations on different transcripts and cells/tissues contexts; available tools to dissect context-specific RNA modifications are still limited. Herein, we report the detailed protocol for using a chemically inducible and reversible platform to achieve site-specific editing of the chosen RNA modification in a temporally controlled manner by integrating the clustered regularly interspaced short palindromic repeats (CRISPR) technology and the abscisic acid (ABA)-based chemically induced proximity (CIP) system. The procedures were demonstrated using the example of inducible and reversible N6-methyladenosine (m6A) editing and the evaluation of its impact on RNA properties with ABA addition and reversal with the control of ABA or light.

0 Q&A 71 Views Feb 5, 2023

Single-nucleus RNA sequencing (snRNA-seq) provides a powerful tool for studying cell type composition in heterogenous tissues. The liver is a vital organ composed of a diverse set of cell types; thus, single-cell technologies could greatly facilitate the deconvolution of liver tissue composition and various downstream omics analyses at the cell-type level. Applying single-cell technologies to fresh liver biopsies can, however, be very challenging, and snRNA-seq of snap-frozen liver biopsies requires some optimization given the high nucleic acid content of the solid liver tissue. Therefore, an optimized protocol for snRNA-seq specifically targeted for the use of frozen liver samples is needed to improve our understanding of human liver gene expression at the cell-type resolution. We present a protocol for performing nuclei isolation from snap-frozen liver tissues, as well as guidance on the application of snRNA-seq. We also provide guidance on optimizing the protocol to different tissue and sample types.

0 Q&A 79 Views Feb 5, 2023

In addition to cytosolic protein synthesis, mitochondria also utilize another translation system that is tailored for mRNAs encoded in the mitochondrial genome. The importance of mitochondrial protein synthesis has been exemplified by the diverse diseases associated with in organello translation deficiencies. Various methods have been developed to monitor mitochondrial translation, such as the classic method of labeling newly synthesized proteins with radioisotopes and the more recent ribosome profiling. However, since these methods always assess the average cell population, measuring the mitochondrial translation capacity in individual cells has been challenging. To overcome this issue, we recently developed mito-fluorescent noncanonical amino acid tagging (FUNCAT) fluorescence-activated cell sorting (FACS), which labels nascent peptides generated by mitochondrial ribosomes with a methionine analog, L-homopropargylglycine (HPG), conjugates the peptides with fluorophores by an in situ click reaction, and detects the signal in individual cells by FACS equipment. With this methodology, the hidden heterogeneity of mitochondrial translation in cell populations can be addressed.

Protocols in Past Issues
0 Q&A 205 Views Jan 20, 2023

In this study, we introduce a detailed protocol for the preparation of DNA-assembled GRS-DNA-copper sulfide (CuS) nanodandelion, a multifunctional theranostics nanoparticle. Using transmission electron microscope (TEM) and dynamic light scattering techniques, we characterize the physicochemical property of DNA-assembled GRS-DNA-CuS nanodandelions and their dissociation property after the first near-infrared (NIR) light irradiation. In addition, we systematically monitor the processes of tumor accumulation and uniform intratumoral distribution (UITD) of ultrasmall CuS photothermal agents (PAs), which are dissociated from GRS-DNA-CuS nanodandelions, by Raman imaging and photoacoustic imaging, respectively. The UITD of the dissociated ultrasmall CuS PAs can enhance the therapeutic efficiency of photothermal treatment under the second NIR light irradiation. Overall, this protocol provides a powerful tool to achieve UITD of PAs by explosively breaking the hydrogen bonds of DNA in GRS-DNA-CuS nanodandelions under NIR light irradiation. We expect DNA-assembled nanotheranostics to serve as a robust platform for a variety of biomedical applications related to photothermal therapy in the oncology field. This protocol can increase experimental reproducibility and contribute to efficient theranostics nanomedicine.

0 Q&A 290 Views Jan 5, 2023

Utilizingresources available from the mother's body to guarantee healthy offspring growth is the fundamental reproductive strategy. Recently, we showed that a class of the largest extracellular vesicles known as exophers, which are responsible for the removal of neurotoxic components from neurons (Melentijevic et al., 2017) and damaged mitochondria from cardiomyocytes (Nicolás-Ávila et al., 2020), are released by the Caenorhabditis elegans hermaphrodite body wall muscles (BWM), to support embryonic growth (Turek et al., 2021). Employing worms expressing fluorescent reporters in BWM cells, we found that exopher formation (exophergenesis) is sex-specific and fertility-dependent. Moreover, exophergenesis is regulated by the developing embryo in utero, and exophers serve as transporters for muscle-generated yolk proteins, which can be used to nourish the next generation. Given the specific regulation of muscular exophergenesis, and the fact that muscle-generated exophers are much larger than neuronal ones and have different targeting, their identification and quantification required a modified approach from that designed for neuronal-derived exophers (Arnold et al., 2020). Here, we present a methodology for assessing and quantifying muscle-derived exophers that can be easily extended to determine their function and regulation in various biological contexts.


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0 Q&A 137 Views Jan 5, 2023

Advances in imaging technology offer new opportunities in developmental biology. To observe the development of internal structures, microtome cross-sectioning followed by H&E staining on glass slides is a common procedure; however, this technique can be destructive, and artifacts can be introduced during the process. In this protocol, we describe a less invasive procedure with which we can stain insect samples and obtain reconstructed three-dimensional images using micro-computed tomography, or micro-CT (µCT). Specifically, we utilize the fungus-farming ambrosia beetle species Euwallacea validus to observe the morphology of mycangia, a critical internal organ with which beetles transport fungal symbionts. Not only this protocol is ideal to observe mycangia, our staining/scanning procedure can also be applied to observe other delicate tissues and small organs in arthropods.


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0 Q&A 255 Views Jan 5, 2023

RIBO-seq and proteogenomics have revealed that mammalian genomes harbor thousands of unannotated small and alternative open reading frames (smORFs, <100 amino acids, and alt-ORFs, >100 amino acids, respectively). Several dozen mammalian smORF-encoded proteins (SEPs) and alt-ORF-encoded proteins (alt-proteins) have been shown to play important biological roles, while the overwhelming majority of smORFs and alt-ORFs remain uncharacterized, particularly at the molecular level. Functional proteomics has the potential to reveal key properties of unannotated SEPs and alt-proteins in high throughput, and an approach to identify SEPs and alt-proteins undergoing regulated synthesis should be of broad utility. Here, we introduce a chemoproteomic pipeline based on bio-orthogonal non-canonical amino acid tagging (BONCAT) (Dieterich et al., 2006) to profile nascent SEPs and alt-proteins in human cells. This approach is able to identify cellular stress-induced and cell-cycle regulated SEPs and alt-proteins in cells.


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Schematic overview of BONCAT-based chemoproteomic profiling of nascent, unannotated small and alternative open reading frame-encoded proteins (SEPs and alt-proteins)

1 Q&A 247 Views Jan 5, 2023

Sclerotinia sclerotiorum causes white mold, leading to substantial losses on a wide variety of hosts around the world. Many genes encoding effector proteins play important roles in the pathogenesis of S. sclerotiorum. Therefore, establishment of a transformation system for the exploration of gene function is necessarily significant. Here, we introduce a modified protocol to acquire protoplasts for transformation and generate knockout strains, which completements the transformation system of S. sclerotiorum.


0 Q&A 328 Views Dec 20, 2022

MicroRNAs (miRNA) are small (21–24 nt) non-coding RNAs involved in many biological processes in both plants and animals. The biogenesis of plant miRNAs starts with the transcription of MIRNA (MIR) genes by RNA polymerase II; then, the primary miRNA transcripts are cleaved by Dicer-like proteins into mature miRNAs, which are then loaded into Argonaute (AGO) proteins to form the effector complex, the miRNA-induced silencing complex (miRISC). In Arabidopsis , some MIR genes are expressed in a tissue-specific manner; however, the spatial patterns of MIR gene expression may not be the same as the spatial distribution of miRISCs due to the non-cell autonomous nature of some miRNAs, making it challenging to characterize the spatial profiles of miRNAs. A previous study utilized protoplasting of green fluorescent protein (GFP) marker transgenic lines followed by fluorescence-activated cell sorting (FACS) to isolate cell-type-specific small RNAs. However, the invasiveness of this approach during the protoplasting and cell sorting may stimulate the expression of stress-related miRNAs. To non-invasively profile cell-type-specific miRNAs, we generated transgenic lines in which root cell layer-specific promoters drive the expression of AGO1 and performed immunoprecipitation to non-invasively isolate cell-layer-specific miRISCs. In this protocol, we provide a detailed description of immunoprecipitation of root cell layer-specific GFP-AGO1 using EN7::GFP-AGO1 and ACL5::GFP-AGO1 transgenic plants, followed by small RNA sequencing to profile single-cell-type-specific miRNAs. This protocol is also suitable to profile cell-type-specific miRISCs in other tissues or organs in plants, such as flowers or leaves.


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0 Q&A 623 Views Dec 20, 2022

CRISPR/Cas9 screening has revolutionized functional genomics in biomedical research and is a widely used approach for the identification of genetic dependencies in cancer cells. Here, we present an efficient and versatile protocol for the cloning of guide RNAs (gRNA) into lentiviral vectors, the production of lentiviral supernatants, and the transduction of target cells in a 96-well format. To assess the effect of gene knockouts on cellular fitness, we describe a competition-based cell proliferation assay using flow cytometry, enabling the screening of many genes at the same time in a fast and reproducible manner. This readout can be extended to any parameter that is accessible to flow-based measurements, such as protein expression and stability, differentiation, cell death, and others. In summary, this protocol allows to functionally assess the effect of a set of 50–300 gene knockouts on various cellular parameters within eight weeks.


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0 Q&A 514 Views Dec 20, 2022

Cloning systems like Gateway and Golden Gate/Braid are known because of their efficiency and accuracy. While the main drawback of Gateway is the expensive cost of the enzymes used in its two-step (LR and BP) reaction, Golden Gate requires non-reusable components due to their specific restriction sites. We present the Brick into the Gateway (BiG) protocol as a new cloning strategy, faster and more economic method that combines (i) reusable modules or bricks assembled by the GoldenBraid approach, and (ii) Gateway LR reactions [recombination of attachment sites: attL (L from left) and attR (R from right)] avoiding the BP reaction [recombination of attachment sites: attP (P from phage) and attB (B from bacteria)] usually necessary in the Gateway cloning. The starting point is to perform a PCR reaction to add type IIS restriction sites into DNA fragments generating specific fusion sites. Then, this PCR product is used to design GoldenBraid bricks, including the attL Gateway recombination sites. Using the Golden Gate method, these bricks are assembled to produce an attL1–gene of interest–attL2 fragment, which is integrated into a compatible vector producing a Gateway entry vector. Finally, the fragment containing the target gene is recombined by LR reaction into the Gateway destination vector.


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0 Q&A 1174 Views Dec 5, 2022

RNA is a vital component of the cell and is involved in a diverse range of cellular processes through a variety of functions. However, many of these functions cannot be performed without interactions with proteins. There are currently several techniques used to study protein–RNA interactions, such as electrophoretic mobility shift assay, fluorescence anisotropy, and filter binding. RNA-pulldown is a technique that uses biotinylated RNA probes to capture protein–RNA complexes of interest. First, the RNA probe and a recombinant protein are incubated to allow the in vitro interaction to occur. The fraction of bound protein is then captured by a biotin pull-down using streptavidin-agarose beads, followed by elution and immunoblotting for the recombinant protein with a His-tag–reactive probe. Overall, this method does not require specialized equipment outside what is typically found in a modern molecular laboratory and easily facilitates the maintenance of an RNase-free environment.


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